Process for manufacture of wallboard from lignocellulosic material



Patented Jan. 9, 1951 raocrzss FOR MANUFACTURE, or WALL- BOARD FROMLIGNOCELLULOSIC MATE- RIAL Warren R. Smith, Crown Point, N. Y., andDonald F. Othmer, Coudersport, Pa.: said Smith assignor to Donald F.Othmer, William R. White, Jr., and Louis Ricciordi No Drawing.Application June 8, 1948, Serial No. 675,444

3 Claims. 1

Qur invention relates to a process for producing a hard, dense, strongwater-resistant wall board and other products from lignocelluloslcmaterials by the application of controlled heat and pressure for arelatively short length of time to a mixture of such lignocellulosicmaterials and added materials.

Various types of wall boards have been made by the application of heatand pressure to lignoce lulosic materials obtained in a more or lessfibrous form by other preliminary operations. These processes have hadto use raw wood, rather than short fibre waste material, such assawdust. These wall boards are inherently expensive because of the valueof the wood and of the cost of the mechanical and chemical operationsfor reducing to a fibrous state.

In these processes the fibres prepared by mechanical and chemicaltreating operations have been made in a slurry with water and runthrough a screen to form a wet lap which is then submitted to thesubsequent pressing operations. These processes require a screen box,wherein the water drains out the screen forming the bottom, to leave asheet of the wet lap the size of the box, or, alternatively, apaper-making machine, such as a fourdrinier, wherein the sheet is formedcontinuousiy on a moving screen belt.

Where it has been suggested to use chemical substances as additions tothe slurry or the otherwise prepared flbrous material, it has been foundnecessary to subject such chemical substances to a special treatment tobring out or increase its bonding properties, as for instance, by usingthe distillate of certain acid substances.

The mixture formed between such chemical substances and the ligneousmaterial, where used in a dry form, was not considered fit to beintroduced into the press to form the des red final product without anumber of intermediate steps in succession, such as storing for acertain length of time, preforming into mats, drying the mats, pilingthe thus formed material, etc.

In particular, where in such multistep process lignin has been reactedwith phenols or, replacing the phenols, with cresols, the ensuing ligninplastics have always proved of very poor quality and have in no wisebeen suited as wall boards and similar structures in which a highrupture modulus is imperative.

It is, therefore, an object of this invention to make a wall board orsimilar hard, dense, strong and water-resisting product from waste woodsubstances which have had no chemical or me- Another object of theinvention is the making of such an article by handling only dry orrelatively dry material. in a. pulverulent, granular or fibrous formdirectly and without the making of such material into a slurry orsuspension for handling in a wet state.

A further object is to allow the use of sawdust, shavings, and othermill waste directly as it comes from the saw, or other wood formingmachine, in a simple, readily operated process, with a minimum of stepsand equipment so that such manufacturing operations may be conducted byrelatively small plants in isolated places and with a minimum oftechnical skill.

A particular object in this invention is to use not only thelignocellulosic material as it comes from the factory, but also to usethe chemical materials in their crude form without special preliminarytreatment.

We have now found that when cresylic acid is added to the fibrousmaterials as it comes as waste from other operations, for instance, tosawdust by a relatively simple mixing operation, the material can thenat once and without intermediate treatment be pressed at a suitablepressure and temperature to give a hard wa l board of propertiescomparable to those obtained by more complicated methods of manufacture.

This surprising effect may be due to the fact that the cresylic acidactivates or catalyzes the bonding action of lignin in thelignocellulosic materials so that it serves as a bonding agent in thefinished board to make a hard, dense, strong material. The cresylic acidmay be sprayed onto the sawdust after or without adding additionallignin to it.

Another activating agent is phenol which preferably is used in the formof carbolated petrolatum which contains a substantial portion of phenol.Also xylenol has been found useful as an activating agent in ourprocess.

It is also possible to add certain other materials besides ouractivating agents to the board in order to increase the strength orwater resistance or the fire resistance of the boards. In particular,the addition of mineral oils such as petrolatum and other similarsemi-solid or solid hydrocarbons gives a product which is more waterresistant.

We have also found it advantageous to add additional lignin in somecases, such additional lignin coming from one of the various sources oflignin available, 1. e., from the waste liquors discharged in thevarious processes for making wood chanical treatment prior to thepresent operation. 56 pulp for use in making paper, etc., and from the 3residual solids left after hydrolysis of the cellulose in wood for themaking of fermentablesugars for alcohol production, etc.

The lignocellulosic material used in our process may be wood fromdeciduous or coniferous trees or from other plants than trees. The sizesof the small wood particles may vary considerably so that the waste fromdifferent wood converting processes may be used including shavings fromplaners, different sizes of sawdust from ripsaw and re-sawingoperations, cross sawing, etc... etc. In general, it is desirable to useparticles having a maximum thickness of not over about 9;" and in manycases a finer material is preferable.

In general, we would use the fibers containing the normal amountofmoisture present in them without drying; and, in fact, we prefer touse a material containing from 5 to 30% water, and up to as much as 50%.Such an amount of water is hardly appreciable mechanically since thematerial acts as a pulverulent granular material as distirguished fromthe slurry used in other processes where thematter is in a watersuspension containing only one or two percent of fiber.

We would mix the preferred chemical material by spraying if the addedchemical is a liquid; or by solid mixers for powder if all the materialsare powdered. Any suitable device which gives a substantially uniformmixture of the chemical material with the ceilulosic material may beused.

Having formed the mixture, it is necessary to press under suitableelevated temperature the cellulosic material; and since there will besome moisture to be discharged as well as some gases due to the chemicalactions involved, it is necessary to make provision for the discharge ofsuch gases. One suitable manner which has been described in greaterdetail in one co-pending application, Serial No. 627,092, filed November6, 1945, and now abandoned, is to place the material between the platensof the press, wherein one platen is either smooth itself or has a smoothplate between it and the cellulosic material; and the other platen hasone or more wire screens in contact therewith (or other similar device)so that gases may work their way to the edge of the platen through andaround the meshes of the wire screen or similar device and thus escape.

In some cases when relatively thick boards or ob- Jects of other formshaving relatively thick sections are to be made, we may use screens orother similar arrangements on both platens so as to allow the dischargeof gases from both surfaces.

The sawdust or the ceilulosic material mixed with the activating agentlike cresylic acid or phenol acid is pressed for a period of from 7 to20 minutes, preferably 11 to 13 minutes, with a temperature on theplatens in the neighborhood of 178 to 300 0., preferably 245 to 155 C.The pressure may range from approximately 150 lbs. per square inch toany higher value desired but we have found that in the usual casepressures below about 500 lbs. per square inch are entirely adequatealthough for some purposes we may wish to go as high as 1000 lbs. persquare inch. The pressure may be constant but for a number of materialsand certain operating conditions it is desirable to gradually build upthe pressure during the operation from about 100 to about 500 lbs. persquare inch.

There is an inter-relation of the three variables of time, temperatureand pressure; and, keeping time constant, a higher temperature on theplatens may give the same result at a somewhat lower pressure; or, ifthe pressure is kept constant, a higher temperature may give this sameresult in a somewhat lower time. There is required the time to heat thematerial to a temperature somewhat lower than or approximating that ofthe platen itself; and the time for this heat transfer will also bereduced by an increase in the pressure due to a compacting of thefibrous material. Beside the time for the heat transfer in heating upthecharge, there is also required some time for the chemical conversion ofthe lignin and the production of the binding qualities thereby.

Good results have been obtained, for instance, on" the following basis;600 grams sawdust per square foot with a moisture content of 10-15% weremixed, for instance, by mixing, with 20 grams cresylic acid and 48 gramslignin. This mixture was then subjected to a pressure of 500 lbs. persquare inch during a Period of 12 minutes and at an average temperatureof 235 C.

In a modification of this same process and using the same materials, thepressure was gradually increased, starting with lbs. and going up to 500lbs. per square inch.

A variation of the original composition produced likewise highlysatisfactory results. In this instance the pressure was kept constantbut the cresylic acid content was augmented so that it amounted to 60grams while the lignin was cut to 20 grams per square foot. The averagetemperature in this instance was 240 C.

Other examples showing the percentage of activating agent to be addedappear from the following table which also indicates the rupture modulusin the last column.

Rupture Lignin (Indulln) 3.37 Lignin 33 Lir nin phenbl 0.20%

In gnlinis the trade-mark for commercially available 8 Whereas we haveshown the advantage of the use of certain types of activating agents inthe production of a wallboard made directly from sawdust, we have alsonoted that these same activating agents may be added equally well tosimilar articles manufactured by other processes and with equaladvantage. Thus, for example, in the manufacture of wallboard byexploding wood ghips to give a fibrous mass which then may be formedinto a board by suitable and known means, we have found that theaddition of our activating agents for the lignin produces a betterproduct than can be produced otherwise and without its use. Similarly,in the production of plastic materials from ligno-celiulose formed bythe partial hydrolysis of wood (see for example the paper in I. and E.C., by Raphael Katzen and Donald F. Othmer, vol. 34, page 314, March1942) the use of our preferred materials for activating the ligninresults in substantial advantage if added to the molding powder asusually prepared for use in makingmolded objects.

We have also found that many other shapes and types of. articles besideswall board may be made by our method or reactivating the-lignin orfacture because of its tremendous volume of business, our mixtures ofmaterials and our methods of operation as described above and with onlyminor and self-evident modifications may be employed for making numerousother forms of finished articles. Instead of being formed between flatplatens, dies of many patterns may be used with appropriate design andoperation to take care of the characteristics of the materials asdescribed above. Panels, doors, counter tops, and many types ofarchitectural shapes as well as a wide variety of molded objects may befabricated. From this standpoint our invention may be regarded asencompassing a molding powder, as the term is used in the trade. Also,while we refer to wall board as the principal type of manufacturedarticle made hereby, it should be under stood that all of these otheritems which may be made by modifying the shapes of the dies are likewiseincluded.

Thus, the cellulosic short-fibred material, such as sawdust withactivator, may be laid or piled upon the surface of the ply woodassemblage before the assemblage goes to the press. The heat andpressure normally employed for bonding the ply wood units produces anoverlay surface thereon. This method has particular utility whereperfect top layers in the ply wood assembly are not available, andrough, un-planed lowgrade boards, used in ply wood assembly, may beconverted to smooth surfaced member, all im* perfections being covered.

Low grade or rough surfaced planed or unplaned lumber, particularlylumber having imperfections such as cracks, knots, checks, etc., may beprovided with improved surface characteristics and up-graded, bysimilarly coating one or both surfaces of such lumber by means of ourprocess. In such application of our method, a further utility may berealized due to the presence of the activating agent in its tendency torepel insect attack. It will also be understood that such effect can beaugmented by the addition of germicidal, fungicidal and insect-repel- Ilant materials.

Having thus described our invention, what we claim and desire to secureby Letters Patent is as follows:

1. A process for making wallboard comprising adding an activating agentof the group consisting of phenol, cresol, xylenol, and mixturesthereof, to lignin admixed with natural lignocellulosic material, in theproportion of 2.6% to 10% of activating agent and 3.3% to 10% of lignin,based on the weight of the lignocellulosic material, the amount of waterpresent being no more than that occurring in the lignocellulosic 2material in its naturally occurring state, followed by the steps ofsubjecting the mixture of activat ing agent, lignin and lignocellulosicmaterial to heat and pressure between platens, the temperature of saidplatens being between 178 C. to 300 C, the pressure being at leastpounds per square inch.

2. A process for making wallboard comprising adding an activating agentof the group consisting of phenol, cresol, xylenol, and mixturesthereof, to lignin, said lignin consisting of lignin obtained from woodpulp producing processes, admixed with natural lignocellulosic material,in the proportion of 2.6% to 10% of activating agent and 3.3% to 10% oflignin, based on the weight -of the lignocellulosic material, the amountof water present being no more than that occurring in thelignocellulosic material in its naturally occurring state, followed bythe steps of subjecting the mixture of activating agent, lignin andlignocellulosic material to heat and pressure between platens, thetemperature of said platens being between 178 C. to 300 C., the pressurebeing at least 150 pounds per square inch.

3. A process for making wallboard comprising adding an activating agentof the group consisting of phenol, cresol, xylenol, and mixturesthereof, to lignin, said lignin consisting of the residual lignin solidsobtained after the partial hydrolysis of wood, admixed with naturallignocelulosic material in the proportion of 2.6% to 10% of activatingagent and 3.3% to 10% of lignin, based on the weight of thelignocellulosic material, the amount of water present being no more thanthat occurring in the lignocellulosic material in its naturallyoccurring state, followed by the steps of subjecting the mixture ofactivating agent. residual lignin solids and lignocellulosi': materialto heat and pressure between platens, the temperature of said platensbeing between 178 C. to 300 C., the pressure being at least 150 poundsper square inch.

WARREN B. SMITH. DONALD F. OTHMER.

REFERENCES CITED UNITED STATES PATENTS Number Name Date 1,721,315Novotny July 16, 1929 1,923,756 Sherrand Aug. 22, 1933 2,036,156Lundback Mar. 31, 1936 2,156,160 Olson Apr. 25, 1939 2,180,547 PetersonNov..21, 1939 2,247,209 Schorger June 24, 1941 2,283,821 Schorger May19, 1942 2,319,951 Schorger May 25, 1943 Schorger May 25, 1943

1. A PROCESS FOR MAKING WALLBROAD COMPRISING ADDING AN ACTIVATING AGENTOF THE GROUP CONSISTING OF PHENOL, CRESOL, XYLENOL, AND MIXTURESTHEREOF, TO LIGNIN ADMIXED WITH NATURAL LIGNOCELLULOSIC MATERIAL, IN THEPROPORTION OF 2.6% TO 10% OF ACTIVATING AGENT AND 3.3% TO 10% OF LIGNIN,BASED ON THE WEIGHT OF THE LIGNOCELLULOSIC MATERIAL, THE AMOUNT OF WATERPRESENT BEING NO MORE THAN THAT OCCURRING IN THE LIGNOCELLULOSICMATERIAL IN ITS NATURALLY OCCURRING STATE, FOLLOWED BY THE STEPS OFSUBJECTING THE MIXTURE OF ACTIVATING AGENT, LIGNIN AND LIGNOCELLULOSICMATERIAL TO HEAT AND PRESSURE BETWEEN PLATENS, THE TEMPERATURE OF SAIDPLATENS BEING BETWEEN 178* C. TO 300* C., THE PRESSURE BEING AT LEAST150 POUNDS PER SQUARE INCH.